This invention relates in general to a control system for an internal combustion engine with turbocharger, and more specifically to a governing system to limit engine speed and output torque in response to certain operating conditions.
In the field of internal combustion engines, the self-limiting characteristics of the unsupercharged or normally aspirated petrol engine will usually prevent excessive engine speed. In most cases, the self-limiting characteristics establish a balance between the torque required to overcome friction and windage losses and the torque developed in the unloaded engine at full throttle at a speed sufficiently low to prevent self-destruction. However, in applications where an air supercharging device is used to increase engine output a maximum engine speed limiting device becomes a virtual necessity. Typically, a governor is the device used to control the maximum engine speed.
A governor can be a mechanical or electromechanical device for automatically controlling the speed of an engine by regulating the intake of fuel. The governor limits the amount of fuel delivered to the engine once a predetermined engine speed is reached. When an engine is operated close to the governor engine speed setting, the engine speed oscillates above and below the governor setting due to delays in engine response to the reduction in fuel. Oscillation around the governor engine speed setting is an undesirable operating condition known as "hunting".
The simplest method of achieving stability in the system and eliminating hunting is to add a control system that will provide speed droop in the governor. Speed droop is a sharp decrease in engine output torque above the governor set point. The sharp decrease in output torque caused by the speed droop of the governor acts to provide stability at the governor set point.
Speed droop in a simple mechanical governor can be provided by a mechanical interconnection between servo movement and governor speed setting such that, as fuel is increased, the speed setting is decreased. The servo is positioned in response to movement of the throttle. Such a device may consist simply of a lever of suitable ratio between servo and speeder spring. The equilibrium relationship between speed setting and servo position for such a system may be represented by a line sloping or "drooping" downward to indicate a lower speed setting with movement of the servo toward the higher fuel delivery position.
While the governing systems placed on internal combustion engines provide overspeed protection and the desired droop curve, there is the added cost and expense of installing a separate governor. This extra expense is sometimes prohibitive, especially on economy class model vehicles. Further, engines with separate governing systems require additional maintenance, resulting in increased costs.
It would be desirable to provide a governing system which uses components of existing engine control systems. The use of existing components will reduce the cost of governing systems and reduce maintenance costs for the engine.